1. Field of the Invention
This invention relates to a unit for interrupting normal operation of an electrical circuit in which a control relay is actuated by a time clock. More particularly, it relates to such a unit which will interrupt the normal operation of the circuit in the next cycle of a plurality of cycles defined by the time clock when the unit is actuated during a particular cycle. Most especially, it relates to such a unit which can be installed between the time clock and control relay of an existing circuit without substantial modification to either.
2. Description of the Prior Art
Most business and commercial buildings have various electrical circuits, such as those used for operating heating and cooling systems for the buildings, which are automatically controlled by time clocks to provide required heating or cooling during normal business hours each day. It has long been recognized that it is desirable to override such normal operation of these systems during weekends, holidays and other special occasions when the usual daily business is not carried out. For example, a manual override switch provided as part of a time clock for this purpose is disclosed in Smith, U.S. Pat. No. 1,981,282 and Klein, U.S. Pat. No. 2,890,300.
It is also known to provide time clocks for such circuits that will automatically skip normal operation without requiring manual setting each time this is to be done. Such time clocks typically incorporate pins or similar members for interfering with normal operation of cams on pre-selected days of a week. Such an arrangement is disclosed in, for example, Klein et al, U.S. Pat. No. 2,921,149 and Prewarski et al, U.S. Pat. No. 3,929,284. While the approach of the latter two patents has achieved acceptance for new installations, particularly in buildings large enough to have full time maintenance employees, it is neither suitable for installation on existing time clock circuits without replacing the entire time clock mechanism, nor is it suited for use in small or medium sized commercial buildings which do not have full time maintenance employees for setting such mechanisms. Problems are encountered when individuals unfamiliar with the time clock mechanism attempt to set the day-skipping controls, both from improper setting and exposure to electrical shock hazards. A need therefore exists for improvement in day-skipping mechanisms for use with time clock controlled electrical circuits to overcome these problems.